LONDON (Reuters) - Iran, under fire from Western powers over its atomic program, on Friday criticized Britain's plans to renew its nuclear arsenal as a "serious setback" to international disarmament efforts.

"Britain does not have the right to question others when they're not complying with their obligations" under the nuclear Non-Proliferation Treaty, Ali Asghar Soltanieh, Iran's envoy to the International Atomic Energy Agency, said at a conference.

Britain's parliament backed Prime Minister Tony Blair's plans to renew the country's Trident nuclear weapons system on Wednesday. Opposition votes helped Blair survive a major rebellion by members of his own party.

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Some within Blair's Labour party had argued that the decision would send the wrong message to states such as Iran and North Korea, which have drawn strong international pressure over their own nuclear programs.

Iran says its nuclear program is peaceful, not to make weapons, but faces new U.N. sanctions after refusing to halt potentially weapons-related nuclear fuel work.

"It is very unfortunate that the UK, which is always calling for non-proliferation ... not only has not given up the weapons but has taken a serious step toward further development of nuclear weapons," Soltanieh told a conference examining the Trident decision.

Blair argued Britain must renew its nuclear weapons because potential threats from countries such North Korea and Iran or terrorists armed with nuclear weapons made it unwise and dangerous to disarm.

He said if Britain were to give up its nuclear weapons it would not improve prospects of other countries disarming.

But Soltanieh said the British prime minister was misleading the public by using Iran's nuclear ambitions to justify the Trident decision. He said that was not the real problem.

"UK security is threatened ... by interfering in international affairs, from occupation and invasion (in the Middle East)," he said. "Is the UK going to use Trident against Al Qaeda? I doubt it."